After considerable work on the Zerochromat design, we now have a very interesting system! There is almost no lateral colour across a 0.7 degree field of view with our 8 inch f12 design. The spot size is diffraction-limited on-axis.
Now we come to the price - a complete tube assembly with electronic focuser is being offered at US$6000. If you are a keen ATM person, the complete optical set is US$2500. We can even offer the corrector optics at US$900 per set - the objective lens and fold mirrors are simple to make for an experienced mirror maker. Please email me on peterwise47@gmail.com for more info.

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If you are keen to make your own telescope from our optics, and you are able to maintain a positioning accuracy of better than 50 microns (2 thou') for the corrector elements, then the rest is easy! Collimation is simple, starting with a laser collimator, and then visually.The theoretical Strehl ratio is 0.98, with an on-axis spot size of 7.8 microns (diffraction limit is 8.2 microns).

Longitudinal colour is very much less important than lateral colour. Longitudinal aberrations can be focused through, but lateral aberrations are apparent in the eyepiece, which is why we have concentrated on this aspect.These designs are excellent visually, but care needs to be taken when imaging to avoid the extreme blue end of the spectrum. Filters can be used for this.The performance of this design compared with a semi-apo is markedly better. However, at $6,000, you would not expect it to compare with a $200,000 instrument!Unlike top end apo refractors, it is easily transported and set up, and does not need an expensive mount.The whole ethos is to provide an affordable large refractor with very good performance, especially for visual users.

Hi. What are the Star Tests like on the several ZeroChromat / ZeroChromat II 'scopes that you have made so far? At say 250x are you seeing very similar diffraction patterns either side of focus with respect to the brightness of the inner and outer rings, and is the "sharpness" of the pattern the same either side of focus? Any Astigmatism (oval shape to the out of focus diffraction pattern on either side of focus) at 250x with a 12 wave defocus (7.6mm of defocus on either side of focus)?

How does the Airy Disc and ring(s) look at 500x? Can you see a fairly sharp Airy Disc surrounded by a perfectly circular low brightness 1st ring and very faint other ring(s)?

What is the detail like that is visible at 250x on Jupiter? Is there any Chromatic Aberration around the edge of Jupiter at 250x or 500x and if so how much?

Hi, under exceptionally good conditions, I used 600x on a bright star, and saw no chromatic aberration at all, with a textbook perfect Airy disc and very faint rings. No astigmatism or any nasties. Identical each side of (sharp) focus. I have seen Saturn beautifully sharp, with no chromatic aberration either. It works very well for difficult close double stars - at Pex Hill observatory near to Liverpool, I used 300x on Epsilon Bootes, and the stars were separated by inky black sky.Not seen Jupiter as yet, with the weather being terrible this side of the pond, plus other things getting in the way.I will post what can be seen on Jupiter soon, and maybe some images.

By better purchasing of the minor components (I make the objective lenses and flats myself to make sure that they are the right quality), the price of a Zerochromat II is now US$5000, and we have one demo model available at US$3200. But be quick if you want it, as we have already sold the other demo model.